Frequency modulation reproducing system



Sept. i3, 1949. c. M. slNNETT FREQUENCY MODULATION REPRODUCING SYSTEM 2Sheets-Sheet l Filed Sept. 25. 1942 CAPACITY PICKUP FREQU ENCY 0fDISCRIMINATOR CIRCUIT MPLIFIER INVENTOR CHT-:STR slNNl-:TT BY ATTORNEY nc. M. slNNl-:TT FREQUENCY MODULATION REPRODUCING SYSTEM Sept. 13, 1949.

2 Sheets-Sheet 2 Filed Sept. 23. l194:2

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CHESTER M. SANNETTv .CZD n.3 xvi ...@Www

Patented Sept. 13, 1949 FREQUENCY MODULATION REPRODUCING SYSTEM ChesterM. Sinnett, Westmont, N. J., assgnor to Radio Corporation of America, acorporation of Delaware Application September 23, 1942, Serial No.459,375 2z claims.` (c1. 17a-400.4)

My present invention relates to systems for reproducing sound waves, andmore particularly to systems employing frequency modulated signals forproducing audio frequency waves.

In the past, it has generally been proposed to reproduce recorded soundwaves, such as phonograph records, by translating the record impressioninto a reactance variation, the reactance variation being employed tomodulate a high frequency oscillator. The modulated high frequencyoscillations have been demodulated, and the resulting modulation energyhas been reproduced. More specifically it has been proposed to utilize,in connection with a phonograph record, a pickup device of theelectrostatic type, variations in magnitude of the capacity beingemployed to vary the frequency of the high frequency oscillator inaccordance with the modulation amplitude. The frequency modulated waveenergy has been converted into corresponding amplitude modulated waveenergy, and the latter has been rectified so as to permit reproductionof the original modulation signals.

In these systems of the prior art various disadvantages and defects havebecome manifest. The ideal type of reproducing system of the frequencymodulation type should be highly sensitive, of high fidelity, and yetcompact and economical. In reproducing audio frequencies up to 10,000 or12,000 cycles Without the introduction of objectionable surface noise,there are various factors that must be considered. The design of thepickup is very important. Generally, it can be stated that a phonographpickup suitable for a high fidelity system should provide a frequencyresponse throughout the usual audio frequency range, which isproportional to either the amplitude or the velocity of the modulationin the record groove. The sensitivity of the pickup should be such thatthe amplification required between the pickup and the loud speaker isnot so great as to introduce serious microphonic difliculties.

It may be stated to be one of the main objects of my present inventionto provide a frequency modulation network for use with a simplespecially designed pickup, which is adapted to reproduce lateral cutrecords, there being provided a frequency modulated signal which hassuflicient frequency deviation to provide a relatively high audiofrequency output when applied to a simple and economical type offrequency discriminator and rectifier.

It is an important object of this invention to provide a frequencymodulation network for a capacity pickup device of the ribbon type; thefrequency modulation network being characterized by its ability toproduce a relatively high audio frequency output in an economicalmanner; the frequency modulation network consisting of a tube which hasa section thereof functioning as a high frequency oscillator ofessentially constant amplitude and whose frequency is deviated bycapacity variations in the capacity pickup, and there being developed inthe plate circuit of the tube frequency modulated oscillations which aresubsequently converted into audio modulation signals corresponding tothe originally recorded audio signals.

Another object of this invention is to provide a frequency modulationsystem which can be generally employed for any source of audio energywhich is utilized in conjunction with a reactance device, whereby theaudio energy is converted into reactance variations; the reactancevariations being transformed into high frequency oscillator frequencyvariations, and a simple resonant circuit being used as the means forconverting the oscillator frequency variations into changes in theamplitude of signals to be applied to a simple diode.

Still another object of my invention is to provide a relativelyinexpensive and highly sensitive device for reproducing phonographrecords, wherein there is provided an oscillator tube which provideselectronic coupling between a frequency modulation oscillator sectionand a simple discriminator circuit arranged in the output circuit of theoscillator tube.

Yet other objects of my invention are to provide phonograph recordreproducing systems wherein one or more elements of the reproducingcircuits may be located upon the tone arm of the phonograph. v

Still other objects of my invention are to improve generally thesimplicity, efficiency and reliability of recorded sound wavereproducing systems, and more especially to provide a frequencymodulation reproducer for sound records which is not only capable ofproducing high fidelity reproduction substantially free of surfacenoises, but which secures such reproduction in a highly economicalmanner.

The novel features which I believe to be characteristic of my inventionare set forth with particularity in the appended claims; the inventionitself, however, as to both its organization and method of operationwill best be understood by reference to the following description takenin connection with the drawing in which I have indicateddiagrammatically several circuit organizations whereby my invention maybe carried into effect.

In the drawing:

Fig. 1 shows a circuit embodying the invention,

Fig. 2 shows the resonance curve of the dis criminator circuit',

Fig. 3 shows the tone arm with all the elements of the circuit of Fig. lmounted on the tone arm,

Fig. 4 illustrates a modiiied form of construction wherein solely theoscillator tube is mounted on the tone arm,

Fig. 5 shows the circuit diagram of the modification shown in Fig. 4.

Referring, now, to the accompanying drawings, wherein like referencecharacters in the various figures designate similar circuit elements,there is shown in Fig. l a circuit diagram of a preferred formof theinvention. By way of example, the invention is shown applied to acapacity pickup device. The latter is to be understood as being adaptedfor cooperation with a, phonograph record of the usual type. The pickupgenerally comprises a fixed electrode I spaced from a movable electrode2. The spaced electrodes I and 2 provide a condenser whose capacityvaries in accordance with the motion of' a stylus secured to the mobileelectrode. The pickup is schematically represented. It is not a part ofthis invention, and reference is made to my application Serial No.414,305, led October 9, 1941, now Patent No. 2,376,456, granted May 22,1945, for a complete disclosure of the manner of constructing the pickupdevice.

The electrode I may be an insulated brass plate mounted on a metalframe, and the plate acts as the high potential side of the pickup. Tothe metal frame may be secured a thin metal ribbon, the latter may be ina plane parallel to the 'electrode I. The ribbon is placed under tensionin order to increase the natural resonance frequency of the pickup.Preferably, the natural frequency is above 10,000 cycles. Displacementof the stylus laterally, as when running through the record grooves,results in a change in the position of the ribbon with respect to thexed electrode.

The ribbon, or mobile, electrode 2 is the low potential side of thepickup. If desired, the mobile electrode could be the high potentialside of the pickup device. Displacement of electrode 2 causes a changein the capacitance of the pickup. A coaxial cable is employed to couplethe pickup to the input electrode 3 of oscillator tube 4. The cable maybe a high impedance line. The tube 4 is a tube of the 6SA7 type; it hasa cathode 5, a plate 5 and five control grids arranged successively inthe electron stream to the plate. Control grid 3 acts as the oscillatorinput grid. The second, third and fourth grids are tied together; theyare designated by the numeral 'I since they effectively function as asingle electrode. The electrode 'I acts as the oscillator anode.Suppressor grid 8 is grounded inside the tube envelope. Electrodes 'Iand 8 function to diminish any tendency for capacitive coupling betweenthe oscillator and the output.

The coaxial cable has its grounded sheath 9 connected to the mobileelectrode 2, while the axial conductor II) connects the fixed electrodeI to the high alternating potential side of the coil II. The latter ispreferably of the powdered-iron core type. The cathode 5 is returned toan intermediate point on coil II, the latter point being any desiredpoint above the grounded end of the coil which will produce highfrequency oscillations. The adjustable, powdered-iron core of the coilis conventionally represented. The grid 3 is connected to the axialconductor I Il by conden-ser I2 and resistor I3. returns the grid toground.

The coil II is resonated to a desired, mean frequency Fc by the combinednormal capacity of the pickup and the distributed capacity of the,coaxial line. Merely by Way of example, Fc may he given a value of 30megacycles (mc). It is to be understood that when the stylus is in itsnormal position, then the oscillator tuned circuit has the value Fe.Capacitance variations of the pickup, are translated into frequencyvariations of the constant amplitude, high frequency oscillationsproduced by oscillator 5-3-1. The anode I is connected to a source (+B)of direct current through the resistors I4 and I5; the condenser I6bypasses the upper end of resistor I4 for high frequency cur-rents. Inplace of the pentagrid tube there may be used a 6J7 type of tube., Inthe latter, a pentode, only a single screen grid isl employed betweencontrol grid and suppressor grid.

The natural period of the pickup I -2 may aid in the production of highaudio frequency gain. By using a period above 10,000 cycles the audiogain of the system may be highly improved, while the circuit elementsare kept relatively inexpensive. To increase the radio frequency gain,the oscillator section of the tube 4 is electron-coupled tc the platecircuit. Frequency modulation of the oscillations is produced by virtueof the variations in capacity of the oscillator tank circuit.

The recorded sound waves are converted into capacity variations by thepickup device. Hence, the latter variations act to vary the frequency ofthe high frequency oscillations in accordance with the amplitude of therecorded sound waves. The rate of frequency deviation is a function ofthe audio frequencies per se. The extent of frequency deviation, orswing, is dependent upon the audio amplitude. The maximum deviation maybe as high as 1 5 kilocycles (kc.) to either side of Fe, the centerfrequency. Of course, the deviation may Vary depending on the value ofthe chosen mean frequency. The generic expression angularvelocity-modulated is used herein to designate that the modulation ofthe high frequency oscillations may be either frequency or phase. Thelatter type cf modulation differs only in that the rate of deviation forhigher audio frequencies is greater. Furthermore, it is to be clearlyunderstood that this circuit is equally applicable to any desired typeof audio frequency energy source. For example, a microphone pickup mayreplace the phonograph pickup. Further, the microphone may be one usedin hearing-aid apparatus, public address systems, binaural systems andthe like. There are many other applications such as pressure devices,liquid height measuring devices, elongation measurement, vibrationmeasurement, etc. in which the invention may be incorporated.

Those skilled in the art are fully acquainted with the phenomenon ofelectron coupling between an oscillator section of a tube and a moreremote positive electrode thereof. It is believed sufficient for thepurpose of this application to point out that the circuit connected toplate 6 has produced therein the frequency modulated oscillations byvirtue of electron coupling between the oscillator section of tube 4 andplate E. A relatively simple and inexpensive type of` discriminatorcircuit is provided to transform the frequency modulatedoscillationsinto corresponding amplitude modulated oscillations. Duringthis transformation process the frequency deviation of the frequencymodulated wave energy is translated into corresponding amplitudemodulated waves.' This discrimination action is well known. Thediscriminator circuit comprises the powderediron core coil I 1 connectedin shunt with condenser I8. The high alternating potential side ofcircuit I'I-I 8 is connected to plate E. The lower end of coil I'I isconnected by resistor I9 to the junction of resistors I4 and I5. Thejunction of resistors I4 and I5 is bypassed to ground for high frequencycurrents by condenser 2B, and condenser 2l connects the low potentialside of coil I1 `to ground for high frequency currents.

The discriminator circuit I'I-l8 isvmistuned with respect to Fc. Inother words, and referring to Fig. 2, the peak resonance frequency ofcircuit I'I-IB may be higher than the frequency Fc of the oscillatortank circuit. Fig. 2 shows that Fc may be located along the slope ofeither flank of the resonance curve of discriminator circuit I'I|8.Preferably, it is desirable to adjust the iron core of coil I'I so thatthe resonant frequency of the discriminator circuit is such that themean oscillator frequency falls at approximately the 70% response pointon one side of the selectivity characteristic shown in Fig. 2. Hence,the subsequent rectifier will have an input circuit whose operatingpoint is along a linear portion of a singlo-peak resonance curve. Itwill be recognized that such operation results in translation of thefrequency modulated wave energy into correspending amplitude modulatedwave energy.

It is desirable, of course, that the selectivity characteristic, or theQ of the circuit, be so chosen that the slopes of the resonance curveare as linear as possible. Rectification of the amplitude modulated waveenergy is effected by a sirnple diode circuit. To secure further economyof elements with high audio gain, there is employed a diode-triode ofthe 6R7 type. The numeral 22 designates such a tube. The lattercomprises a cathode 23. an anode 24, control grid 25 and a plate 2S. Theanode 24 and cathode 23 function as the rectier diode. The anode 24 isconnected to its cathode through a series path comprising a radiofrequency choke coil 21 and load resistor 28. and across the resistorthere is developed the modulation voltage. nected from the lower end ofcoil 21 to ground, and bypasses all high frequency components. Thecondenser 30 couples the upper end of coil 21 to the high potential sideof the discriminator circuit III8.

The audio modulation voltage, which is developed across resistor 28. isamplied in the triode section of tube 22. This is accomplished byconnecting grid 25 to the anode end of resistor 28 through couplingcondenser 3|, resistor 32 con- 'P necting the grid 25 to the groundedend of the cathode biasing resistor 33. The plate'2B may be connectedthrough the output load resistor 34 to the junction of resistors I4 andl5. In this way there is secured a considerable increase in audiovoltage, and the amplied audio voltage signals developed across resistorV34 are transmitted to a subsequent utilization network. The latter maycomprise additional stages of audio amplification Y followed by a properreproducer. It is pointed out' The condenser 29 is conthat with thistype of system the general hum level is acceptable, and microphonics arereduced to a very lowvalue. Needle noise is substantially eliminated,and reproduction of the recorded sound waves, whether music or speech,is of extremely high fidelity. It is also pointed out that the tubes 4and 22 employed herein are of commercially available types, and arerelatively inexpensive. Indeed, it can be stated that the cost ofmanufacture of the present reproducing system is many times less thanthat of the conventional record reproducers able to approach the highfidelity of reproduction of the present system.

There are advantages in mounting the various circuit components upon thetone arm of the phonograph, and in close proximity to the pickup device.In Fig. 3 I have shown one manner of mounting the circuit components onthe tone arm. It is not believed necessary to describe Fig. 3 in detail,since it is self-explanatory. Each of the corresponding circuitcomponents of Fig. 1 has been appropriately labeled. The pickup deviceand its attachment are not shown in the figure, since such feature isnot a part of the preesnt invention. Reference is made to my aforesaidapplication for such details. However, it will be observed that it ispossible to mount all the circuit components upon the tone arm, and inthat way it is possible to economize on space in the apparatus.

Where it is not desirable to locate the circuit components as shown inFig. 3, it may still be desirable to mount the oscillator tube directlyon the tone arm. For example, a construction as shown in Fig. 4 may giverelatively greater freedom from extraneous noises. Furthermore,increased stability may also be secured by locating only the pickupdevice and the oscillator tube on the tone arm. It is not believednecessary to describe the construction of Fig. 4 in detail, since theiigure is self-explanatory with reference to Fig. 5.

In Fig. 5 I have shown the circuit which would be employed with a tonearm arrangement such as shown in Fig. 4.V Generally, the circuitelements of Fig. 5, which are similar to those of Fig. l, bearcorresponding numerals. The essential feature of Fig. 5 is theutilization of a low impedance line for connecting the tuned platecircuit of tube 4 to the discriminator circuit which is mounted on theamplifier chassis. The high impedance connection in Fig. 4 is shownrunning through successive damping blocks made of resilient insulationmaterial. The oscillator tube projects far enough to permit removalwithout having to take the cover off.

Considering Fig. 5 more specifically, the oscillator coil II is tuned bythe capacity of pickup 2-'I to the center frequency Fe. It will beunderstood that in this case the coaxial cable S-I is not employed. Theplate coil I'I' is of the powdered-iron core type. The distributedcapacity of coil I I is used to resonate the coil to the properfrequency. It would also be possible to resonate this circuit by lumpedcapacity. The iron core is adjusted so that the coil is tuned to Fc.'The rectier-audio ampliiier tube 22 has its diode rectifier electrodescoupled with the discriminator coil 4l). I'his coil is tuned by itsdistributed capacity. Again, a lumped capacity could be used in additionto distributed capacity. The iron core is adjusted so that the meanfrequency Fc is located as shown in Fig. 2. The audio voltage developedacross load resistor 28 is amplified in the triode section of tube 22.The low impedance line 50 couples coils II' and 40. f

yThe low impedance transmission line may comprise a pair of twistedwires. The terminal coil ateach end ofthe linelil is coupled to therespective coils IT and 40,. and vone' of the leads adjacentto these'terminal coils is grounded at eachl end. The'plate and oscillator anodeelectrodes of tube d are connected to' the +B voltage terminal of thedirect current energizing source. It will be noted that the positivevoltage line Sil' runs along the tone arm, then parallel to the lowimpedance line, and then into the amplifier housing ii). Similarly, theheater line B for tube 4 runs along the tone arm, then parallelV tolines B and', and then into the amplier' housing lll).v The dotted linerectangle 90 designates the tone arm, while the dotted line rectangle'lt denotes the amplifier housing. Comparison between Figs. 4 and 5vwillreadily show the manner in which the various energzing connections aremade from the tone arm to the amplier housing. These figures, also, showthe general location of the low impedance line.

By the term low impedance line is meant a line whose impedance isloWcompared to the high impedance line shown connected between the pickupunit and the oscillator tube input grid.v It is advantageous to use thelow impedance twisted pair of wires 5l), because the line may be locatedand positioned in any desired Way (as in Fig. 4) Without causingreiiection along itself. If the line 59 were of a high impedance', as inthe case of the line running from the pickup, then it would have to becarefully protected. The tubing support of the tone arm would have to bedesigned for it.

Comparing the circuit of Fig. 5 with that of Fig. 1, it will be notedthat in Fig. 5 the oscillator plate circuit has frequency modulated os.-cillations developed across the resonant coil I1' Yby virtue of electroncoupling from the oscillator section of the tube to its plate circuit.-Discrimination is obtained by mistuning resonant coil 4U inthe diodecircuit. In Fig. 1 the mistuned discriminator circuit I'l-l8 is locateddirectly in the oscillator plate circuit. It is to be clearly understoodthat itis within the scope of my present invention to remove from thetone arm all of the circuit components, except the pickup device. Inother Words, and referring to the circuit of Fig. 1, all the circuitcomponents shown in the latter may be mounted within a common housing,While the capacity pickup deviceV |-2 is mounted directly on the tonearm.

While I have indicated and described several systems for carrying myinvention into effect, it will be apparent to one skilled in the artthat my invention is by no means limited to the particular organizationsshown and. described, but that many modications may be made withoutdeparting from the scope of my invention.

What I claim is:

1. In combination with a variable capacity pickup device for reproducingphonograph records, an oscillator tube provided with electrodes formingan oscillator section; a resonant circuit tuned to a high predeterminedmean frequency coupled to said oscillator electrodes for generating highfrequency oscillations, said pickup device being connected as part ofsaid resonant circuit whereby variations in pickup capacitance result infrequency modulation of the high frequency oscillations about said meanfrequency; said tube including a positive output electrode Which iselectron coupled to said oscillator section; a resonant discriminatorcircuit connected to said, positivev output electrode, saiddiscriminator circuit having frequency response characteristicsexhibiting a maximum and sloping away on both sides of said maximum;said mean frequency lying at an intermediate portion of one of saidsloping sides; and a rectifier connected directly across saiddiscriminator circuit.

2. In combination with a variable capacity pickup device for reproducingphonograph records, a space discharge tube provided with electrodesforming an oscillator section; a resonant circuit tuned to apredeterminedmean frequency coupled to said oscillator electrodes forgenerating high frequency oscillations, said pick-up device beingconnected as part of said resonant circuit whereby variations in pickupcapacitance result in frequency modulation of the high frequencyoscillations about said means frequency; said tube includneva positiveoutput electrode which is electron coupled to said oscillator section; aresonant discriminator circuit connected to said positive outputelectrode, said discriminator circuit` having frequency responsecharacteristics exhibiting a maximum and sloping away .on both sidesofsaid maximum; said mean frequency lying at an intermediate portion ofone of said sloping sides; and a rectifier tube coupled to saiddiscriminator circuit; said tubes, pickup device and resonant circuitsbeing held on a phonograph tone arm.

3. In combination, a phonograph tone arm provided with a variablereactance phonograph pickup device; a space discharge tube provided withan oscillator section and a positive output electrode, said pickupdevice being connected as part of an oscillator network to saidoscillator section to provide angular velocity-modulated oscillationswhich have Aa predetermined mean frequency; a resonant circuit coupledto said output electrode and tuned to said mean frequency; electroncoupling with said oscillator section through said space discharge tube,to develop amplified angular velocity-modulated oscillations in saidresonant circuit; a line linking said output resonant circuit withanother resonant circuit tuned to a frequency substantially differentfrom said mean frequency to function -as a discriminator circuit; and arectifier connected to said discriminator circuit; said oscillator tubebeing mounted on the tone arm.

4. In combination, a space discharge tube provided With an oscillatorsection and a positive plate electrode; a variable capacity pickupconnected as part of an oscillator network to said oscillator section toprovide frequency-modulated oscillations which have a predetermined meanfrequency; a resonant circuit coupled to said plate electrode forelectron coupling with said oscillator section through said spacedischarge tube to develop said modulated oscillations in said resonantcircuit; said resonant circuit being tuned to a frequency suicientlydifferent from said mean frequency to function as a discriminatorcircuit; and means coupled to said discriminator resonant circuit forrectifying amplitude modulated Wave energy appearing across thediscriminator circuit.

5..In combination with a variable capacity pickup device for reproducingphonograph records, a space discharge tube provided with electrodesforming an oscillator section; a resonant circuit tuned to apredetermined mean frequency coupled to said oscillator electrodes forgenerating high frequency oscillations; said pickup device forming partof said oscillation resonant circuit whereby variations in pickupcapacitance result in frequency modulation of, theA high frequencyoscillations; a discriminator consisting of solely a passive resonantnetwork; means providing electron coupling between the discriminatornetwork and said oscillator section, said discriminator network havingfrequency response characteristics exhibiting a maximum and sloping awayon both sides of said maximum; said mean frequency lying at anintermediate portion of one of said .sloping sides; and a rectifiercoupled to said discrirninator network.

6. In combination with a variable capacity pickup device for reproducingphonograph records, a space discharge tube provided with electrodesforming an oscillator section; a resonant circuit tuned to a highpredetermined mean frequency coupled to said oscillator electrodes forgenerating high frequency oscillations; said pickup device forming partof said oscillation resonant circuit whereby variations in pickupcapacitance result in frequency modulation of the high frequencyoscillations, said tube including a positive output electrode electroncoupled to said oscillator section; a sloping filter discriminatorcircuit connected to said positive output electrode, said mean frequencylying at an intermediate portion of the slope of said lter; and rectiermeans coupled to said discriminator circuit.

7. In combination with a variable capacity pickup device for reproducingphonograph records, a space discharge tube provided with electrodesforming an oscillator section; a resonant circuit tuned to a highpredetermined mean frequency coupled to said oscillator electrodes toprovide high frequency oscillations, a high im'- pedan-ce lineconnecting said pickup device in said resonant circuit wherebyvariations in pickup capacitance result in frequency modulation of thehigh frequency oscillations; said tube including a positive outputelectrode electron coupled to said oscillator section; a discriminatorcircuit, a relatively low impedance line coupling said positive outputelectrode to the discriminator circuit; said discriminator circuithaving frequency response characteristics exhibiting a maximum andsloping away on both sides of said maximum; said mean frequency lying atan intermediate portion of one of the sloping sides; and rectifiermea-ns coupled to said discriminator circuit.

8. In combination with a variable ycapacity pickup device forreproducing phonograph records, a space discharge tube provided withelectrodes forming a high frequency oscillator; a resonant circuit tunedto a high predetermined mean frequency coupled to said oscillatorelectrodes to provide high frequency oscillations; said pickup devicebeing coupled by a high impedance line to form part of said resonantcircuit whereby variations in capacitance result in frequency modulationof the high frequency oscillations; said tube including a positiveoutput electrode electron coupled to said oscillator; a discriminatorcircuit connected to said output electrode, said discriminator circuithaving frequency response characteristics exhibiting a maximum andsloping away on both sides of said maximum; said mean frequency lying atan intermediate portion of one of the sloping sides; a diode rectifiercoupled to said discriminator circuit; and a relatively low impedanceline coupling said positive putput electrode to said discriminatorcircuit.

.9. A system for reproducing signals from a record wherein said signalsare recorded as undulatory impressionszrin the record, comprising: meansfor producing oscillatory waves of a predetermined high meanfrequency; avariable capacity pickup device having a stylus adapted to vibrate inresponse to said record impressions to thereby produce variations inpickup capacitance `representative of said signals; means for frequencymodulating ,said high frequency waves in response to said capacitancevariations; a passive frequency discriminator network coupled to saidwave producing means for translating the frequency modulated waves intocorresponding amplitude modulated waves of like mean frequency; meansproviding electron coupling between saidwave producing means and saidpassive discriminator network; and means for deriving from saidamplitude modulated waves signals corresponding to said desiredmodulation signals.

10. A system for reproducing signals from a record wherein said signalsare recorded as undulatory impressions inthe record, comprising: meansfor producing oscillatory waves of a predetermined highmean frequency; avariable capacity pickup device having a stylus adapted to vibrate inresponse to. said record impressions to thereby produce variations inpickup capacitance representative of said signals; means for frequencymodulating said high frequency waves in response to said capacitancevariations; a passive frequency discriminator network coupled to said.wave producing means for translating the frequency modulated waves intocorresponding amplitude modulated waves of like mean frequency; meansproviding electron coupling between said wave producing means and saidpassive discriminator network; and means for deriving from saidamplitude modulated waves signals corresponding to said desiredmodulation signals, said oscillatory waves having a mean frequency ofthe order of 30 megacycles per second, and said frequency modulatingmeans causing the oscillatory waves to be deviated in frequency up to l5kilocycles per second'vto either side of said mean frequency.

il. A system for reproducing signals in the form of undulatoryimpressions on a record, comprising: means for producing oscillatorywaves of a predetermined high mean frequency; a variable capacity pickupdevice having a stylus adapted to vibrate in response to said recordirnpressions to thereby produce variations in pickup capacitancerepresentative of said signals; means for frequency modulating said highfrequency waves in response to said capacitance variations; a passive,frequency discriminator network coupled to said wave producing meansfor translating the frequency'modulated waves into corresponding"amplitude modulated waves of like mean frequency; means providingelectron coupling between said wave'producing means and said passivediscriminatorV network; means for deriving: from said amplitudemodulated waves signals corresponding to said desired modulation signalsand a tone arm supporting said pickup device and at least saidoscillatory wave producing means.- l

12. In combination with a reactance pickup device for sound records, anelectron discharge tube provided with a cathode, control grid andpositive electrode cooperating to function as an oscillator section, anadditional positive electrode inpsaid tube functioning as an outputelectrode.

'a 'resonant circuit coupledto the oscillator section electrodes, saidresonant circuit being tuned to apredeterminedV high frequency, meansconnecting said pickup device .tosaid resonant circuit wherebyvariations in `pickup reactance result in frequency modulation ofoscillations produced by said oscillator section, a resonant outputcircuit connected to said positive output electrode, said oscillatorsection being electron coupled to said positive output electrode wherebysaid frequency modulated oscillations are applied in amplified form tothe output electrode circuit.

13. In combination with a reactance pickup device for sound records, anelectron discharge tube provided with a plurality of electrodes formingan oscillator section, a resonant -circuit tuned to a predetermined highfrequency coupled to said oscillator electrodes, said pickup devicebeing connected to said resonant circuit whereby variations in pick-upreactance result in frequency I modulation of high frequencyoscillations, said tube including a positive output electrode which iselectron coupled to said oscillator section, a discriminator circuitconnected to said positive output electrode,` said discriminator circuitbeing A tuned to the peak frequency of a resonance curve, saidpredetermined high frequency lying at an intermediate portion of one ofthe slopes of said resonance curve, anda rectifier coupled to saiddiscriminator circuit.

14. In a signal vibration reproducing system: an electron coupledoscillatorA including an electron emissive cathode electrode, anelectron collecting electrode, and electron flow controlling meansincluding at least one electrode grid between the cathode and thecollecting electrode; oscillation supply means including an oscillationfrequency controlling resonant circuit having variable reactance pick-upstructure connected for responding to `vibrational signal variations bycorrespondingly varying its reactance and the tuning of theresonantcircuit in accordance with said signal variations to produce variablefrequency oscillations in which the frequency vlbration correspond tosignal variations; and output means connected to the electron collectingelectrode for utilizing the amplified variable frequency oscillationsdeveloped through the electron coupling between the oscillation supplymeans and the electron collecting electrode; said output means includingdemodulating means for deriving the signal variations from the lvariablefrequency oscillations.

15. The combination asdefined by claim 14 in which the resonant circuitisdirectly coupled to the electrode grid; the demodulating means is inthe form of resonant sloping filter means tuned to a frequency differentfrom the mean frequency of the oscillations; andthe electron flowcontrolling means includes at least one additional electrode gridbetween the collecting electrode and the grid coupled'tothe resonantcircuit, said additional grid rbeing connected for improving the passageof electrons through the grids to the collecting electrode anddiminishing the capactive coupling between adjacent tube elements.

16. The combination as defined by claim 15 in which four electrode gridsare :positioned between the collecting electrode and the grid coupled to.the resonant circuit, and said four :grids are all connected fordiminishing the capactive coupling between the collecting electrode .andthe grid coupled to the resonant circuit.

17. The combination as defined by claim 14 in which the demodulatingmeans includes sloping 12 filter elements cou-pled to produce variableam.- plitudes of response in accordance with variations in output signalfrequency.

.18. The `combination as defined by claim 14 in which the output meansinclude high impedance oscillation transfer elements and a .couplingline having a low impedance with respect to the high .impedanceelements, coupling the collecting electrode to the demodulating means.

19. The combination as defined by claim 14 including a movable tone armholding the pick-up structure, the pickup structure having .of theundulatingly grooved record reproducing type lncluding a stylus forguiding the structure along the grooves of the record to vary the pickupreactance in accordance'with groove undulations; at -lleast part of theVbalance of said reproducing system being also held on said arm.

20. In a phonograph record reproducing sysa tem for reproducing signalsrecorded as undulatory grooves on a solid record: a movable tone armcarrying variably reactive pickup elements including a guide stylus .forguiding the pickup elenients along the grooves and moving the tone armaccordingly; transducing means including khigh-frequency oscillationgenerating structure for developing frequency. modulated electric wavesin which the frequency modulations .corresponds to the signalundulations; and demodulating means for deriving electrical signalscorre,- sponding to the record signals from the frequency modulatedelectric waves; said oscillation generating structure being held by saidmovable tone arm relatively fixed and in relatively close proximity withrespect to the pickup elements.

` 21. In a signal vibration reproducing system: an amplifying electrondischarge tube including an electron emissive cathode, an electroncollecting electrode, and electron flow controlling means forelectrically influencing the movement of electrons from the cathode tothe collecting electrode where they deliver currents corresponding toamplification vof the electrical flow controlling ln.- uences; said flowcontrolling means including at least one electrode grid between thecathode and the collecting electrode; oscillation supply meanscomprising resonant circuit elements, including inductance andcapacitance, coupled with said flow controlling means for producingfrequency modulated oscillations corresponding to the signal vibrationsin the movement of. electrons; said kresonant circuit element beingconnected to lfeed back some `of the amplified energy in the electron4flow to the flow controlling means for producing said oscillations; andoutput means connected to the electron collecting electrode for electroncoupling with said oscillation supply means and developing amplifiedfrequency modulated oscillations; said output lmeans includingdemodulating means for deriving a signal corresponding to the frequencymodulations.

272. In a signal vibration reproducing system; an amplifying electronVdischarge tube including 'an yelectron emissive cathode, an electroncollecting electrode, and electron ow controlling means 'for`electrically influencing the movement o f electrons lfrom the cathodeto the collecting electrode Where lthey deliver currents correspondingto ampli'ication of the electrical flow controlling in.-

fluences;v said flow controlling means'including at least threeelectrode grids between the cathode and the collecting electrode;oscillation supply means coupled -to some of said electrode grids toprovide an oscillator tube section producing frequency modulatedoscillations corresponding to the signal vibrations in the movement ofelectrons; said oscillation supply means being connected to feed backsome of the amplified energy in the electron flow to the ow controllingmeans for producing said oscillations; at least one of said grids beinginterposed between the collecting electrode and said oscillator tubesection and connected to improve the electron flow therebetween; andoutput means connected to the electron collecting electrode for electroncoupling with said oscillation supply means for developing amplifiedfrequency modulated oscillations; said output means including resonantcircuit demcdulating means for deriving a signal corresponding to thefrequency modulations.

CHESTER M. SINNETT.

REFERENCES CITED The following references are of record in the ille ofthis patent:

Number Number 14 UNITED STATES PATENTS Name Date Loewe Aug. 17, 1926 DowJuly 23, 1935 Zakarais July 16, 1940 Crosby Feb. 4, 1941 Zakarias May13, 1941 Farnsworth Dec. 8, 1942 Unger Jan. 23, 1945 FOREIGN PATENTSCountry Date Great Britain Dec. 31, 1932

